Q: Modal developments that happen in song harmonies baffle me. I often see things that don't make sense, like a major IV chord appearing inside of a minor key. I fail to understand why these borrowed chords exist. I'm hoping for a lesson covering harmony shifts & how to treat them melodically?Daniel -- Sydney, Australia

A: Modal harmony shifts can sometimes come across like chromatic harmony. Seeing major and minor chord types get their lines crossed is a common thread for this type of sound. Many of the music theory text-books often only vaguely refer to this idea because it can overall be difficult to say specifically what is being borrowed from where. To get a scope on this, say we went back to the day when music was exclusively melodic - before harmony existed. What actually happened over time, is as music evolved, there became more and more modal limitations. In the end, after these limitations became more distressing, they eventually gave way to a simpler -- now common -- major & minor view of harmony. We still however see these harmony shifts occur in many styles, especially jazz.